Environment protection chiefs in China are being taunted with challenges: cash rewards if they dare to swim in the rivers for which they are responsible.

To no one’s surprise, given the reeking state of many waterways of industrial China, the rewards, offered online, have not been claimed.

The first offer, made this week by the owner of a company in Zhejiang province, was RMB200,000 (£20,000) for 20 minutes in the foetid Rui’an river. Photographs were attached, showing water full of rubbish and seething with orange foam.

Other deals followed: £30,000 for 30 minutes in Cangan county, and £10,000 for a